1. Field of the Invention
The present invention relates to a heating deoiling apparatus for removing machine oil adhering to pieces of work. Also, the present invention relates to a processing oil used for deoiling of aluminum materials after press forming.
2. Description of the Related Art
The manufacturing process of a conventional heat exchanger 20 (see FIG. 2) will be explained below.
The manufacturing process includes: the parts manufacturing step in which parts such as a tube 21, fin 22, tank 23 and header 24 are manufactured; the core assembling step in which the above parts are assembled; the flux coating step in which a portion to be brazed and its periphery are coated with flux; the deoiling step in which machine oil adhering onto a surface of the assembling body is removed; and the brazing step in which the assembling body is brazed, wherein these step are performed in order, so that the heat exchanger 20 can be manufactured. In the above manufacturing process of the heat exchanger 20, the deoiling step is provided for removing machine oil that has adhered onto the surfaces of parts of the assembling body in the parts manufacturing step and the core assembling step, so as to prevent the machine oil from affecting the brazing process to be conducted later. Conventionally, the deoiling step is carried out by a heating deoiling apparatus such as the one illustrated in FIG. 1.
Referring to FIG. 1, an example of the heating deoiling apparatus will be explained below. As illustrated in FIG. 3, a work piece (referred to herein as "work W") is composed as follows: A heat exchanger 20 is set on each tray 25. A large number of trays 25 on which the heat exchangers 20 are set are stacked and put on a carrier 26. The thus composed carrier 26 is conveyed by a conveyer 27.
Reference numeral 28 is a heating furnace. A plurality of heating furnaces 28 are aligned in line for heating and evaporating machine oil which has adhered to the heat exchangers 20. To the heating furnaces 28, provided are preparation chambers 29 arranged on both end sides thereof. The conveyer 27 successively passes through these preparation chambers 29 and the heating furnaces 28, so that the work W can be conveyed into and conveyed out from the apparatus.
There is provided an entrance (not shown) for the work in a boundary between the heating furnace 28 and the preparation chamber 29. Also, there is provided an entrance between the preparation chamber 29 and the outside. A shutter (not shown) is arranged at the entrance (not shown) for the work in a boundary between the heating furnace 28 and the preparation chamber 29, and preferably a shutter (not shown) is arranged at the entrance between the preparation chamber 29 and the outside. These shutters are opened only when the conveyer is driven so as to permit the work to pass through the entrance.
Each heating furnace 28 is provided with a heating burner 30 for feeding heat to the furnace, and a temperature sensor 31 for detecting the temperature in the heating furnace 28. A temperature signal detected by the temperature sensor 31 is inputted into a controller 100. In accordance with this detection signal, the controller 100 controls an amount of heat outputted from the heating burner 30.
Reference numeral 33 is an exhaust fan for exhausting oil evaporated by the heat of the heating burner 30. Evaporated oil is exhausted outside via an exhaust duct 34. Reference numeral 35 is a combustor arranged in the middle of the exhaust duct 34. The combustor 35 burns the gas containing oil sucked from the heating furnace 28, so that the gas containing oil can be changed into a clean combustion gas.
Reference numeral 37 is an agitating fan for agitating an atmosphere in the heating furnace 28. The agitating fan 37 is arranged in the ceiling portion of each heating furnace 28.
Next, the operation will be described as follows. First, the work W is conveyed by the conveyer 27 from the preparation chamber 29 on the entry side into the heating furnace 28. After the completion of conveyance, the aforementioned shutter not shown in the drawing is closed. Temperature in the heating furnace 28 is detected by the temperature sensor 31, and the temperature signal is sent to the controller 100. In accordance with the temperature signal, the controller 100 controls an amount of heat generated by the heating burner 30 of each furnace.
As a result, oil adhering to each heat exchanger 20 is heated and evaporated. The evaporated oil is sucked by the exhaust fan 33 into the exhaust duct 34 and burned by the combustor 35 arranged in the middle of the exhaust duct 34. In this way, oil can be removed. After that, the above shutter is opened, and the conveyer 27 is driven, and the work W in the furnace 28 arranged on the most right is conveyed into the preparation chamber 29 on the right. Also, the work W is conveyed from the left preparation chamber 29 into the most left furnace 28.
However, in the conventional heating deoiling apparatus, the furnace temperature is controlled only by controlling the combustion conducted in the heating burner 30. Therefore, problems may be encountered when the temperature in the heating furnace 28 is to be maintained in a preferable temperature range. These problems will be described in detail as follows.
First of all, the ignition temperature of this oil is lower than 300.degree. C. Accordingly, from the viewpoint of safety, it is preferable that the furnace temperature is maintained at around 200.degree. C.
Next, in the conventional heating deoiling apparatus, the heat exchanger 20 before the brazing step is bundled with a wire in order to prevent the occurrence of looseness and slippage between parts composing the heat exchanger. Even if the heat exchanger 20 is tightly bundled with the wire, when the temperature is raised to 200.degree. C. or higher than that, the bundled heat exchanger is loosened, because an amount of linear expansion of the wire is larger than an amount of expansion of the heat exchanger 20 before the step of brazing. As a result, a relative displacement is caused between the parts of the heat exchanger, and there is a possibility that the product becomes defective. For this reason, it is preferable that the temperature of the heating furnace 28 is maintained at a value lower than 200.degree. C. for safety.
On the other hand, the evaporation temperature of oil adhering to the parts at the atmospheric pressure is about 140 to 160.degree. C. Therefore, when the furnace temperature becomes lower than this temperature, the evaporation speed of adhering oil is remarkably lowered. Of course, when the residence time of the heat exchanger 20 in the furnace is greatly increased before the step of brazing, it is possible to make up for this decrease of the evaporation speed. However, from the viewpoint of maintaining the productivity of the apparatus, it is actually impossible to increase the residence time of the heat exchanger 20 in the furnace.
In order to evaporate the oil adhering to the work before the step of brazing, it can be concluded that the furnace temperature must be maintained in a small temperature range, which is lower than the ignition temperature of the adhering oil and also lower than the temperature at which slippage and looseness can be caused between the bundled parts. Further the temperature range must be higher than the evaporation temperature of the adhered oil.
Because the heat generating power of the heating burner 30 used for the furnace is high, the heating burner 30 is effective for quickly raising the furnace temperature at the start of operation; but, when it is necessary to change the furnace temperature a little, hunting tends to occur in the operation of the burner, and the furnace temperature fluctuates greatly.
Also, the heating burner 30 essentially operates in such a manner that the combustion gas of high temperature not lower than 1000.degree. C. is locally generated by the burner and agitated and mixed so as to be diffused, and the parts of the heat exchanger are heated by its radiation heat. Accordingly, temperature in each portion of the furnace tends to fluctuate in accordance with a gas current in the furnace and a state of radiation heat.
Further, in the conventional heating deoiling apparatus, the combustion gas containing oil generated in the furnace 28 is prevented from leaking outside via the preparation chamber 29 by the shutter not shown in the drawing. However, due to an imperfect air-tightness of the shutter and also due to leaks of the combustion gas caused when the shutter is opened and closed, the combustion gas containing oil leaks out via the preparation chamber 29, that is, it can be smelled outside the furnace.
In order to solve the above problems, air in the preparation chamber 29 may be sucked into the combustor 35, and oil contained in the air is burned in the combustor 35. However, when the above countermeasure is taken, the following problems are caused. Even if a shutter is arranged between the preparation chamber 29 and the outside, an amount of combustion gas flowing into the combustor 35 is increased when this countermeasure is taken. Accordingly, it becomes necessary to provide a combustor 35 of a large capacity, and further its fuel consumption is increased.
When press forming is performed, processing oil is used for improving the sliding property between a die and a piece of work to be subjected to press forming.
In the process of press forming of steel materials, processing oil of high viscosity is used to conduct press forming at a high processing rate. In this case, "the processing rate" is defined as a rate of deformation of a piece of work in the process of press forming. Also, "processing at a high processing rate" is defined as a severe processing step such as a deep drawing of a piece of work of a small diameter. In many cases, an oiliness improver such as an organic acid, the molecular weight of which is relatively large, an ester, and an extreme pressure agent such as chlorination fatty acid are added to the processing oil for processing steel materials. An example of the above processing oil is composed of a base oil belonging to the third petroleum group to which grease, the molecular weight of which is approximately 880, is added. When aluminum materials are processed, the above conventional processing oil for steel materials is also used in many cases.
For the purpose of guaranteeing the quality of products in the processes of brazing, coating, welding and surface treating to be conducted after press forming, pieces of work are subjected to a deoiling process in which the above processing oil is removed. It is necessary to remove both the base oil and the grease of high molecular weight in this deoiling process. Therefore, the following methods are adopted.
(1) Processing oil is removed by water-soluble washing. PA1 (2) Processing oil is evaporated and removed by heating a piece of work. PA1 (3) Processing oil is heated and removed without replacing the processing oil with a light oil. PA1 (4) Processing oil is evaporated by natural drying. PA1 (1) The processing oil for processing aluminum materials belongs to the third petroleum group. PA1 (2) The complete evaporation temperature is not lower than an ordinary room temperature and not higher than 200.degree. C. PA1 (3) The processability is at the same level as that of the conventional processing oil or higher than that. PA1 (4) An oil film can be kept after being left at the ordinary temperature for 72 hours.
Referring to FIG. 4, a case will be explained below in which deoiling is carried out by the above method (1) when aluminum materials are subjected to press forming.
Parts 1, 2 are made by press forming aluminum members. These parts 1, 2 are incorporated into a unit 3. Then the unit 3 is subjected to the process of water-soluble washing, so that the processing oil which has adhered in the process of press forming can be removed. In this process of water-soluble washing, first, the unit 3 is washed in hot water in the water bath 11. Next, in the alkali bath 12 having a plurality of cells 121, 122, 123, 124, the unit 3 is successively moved from the left end cell 121 to the right end cell 124 shown in FIG. 4. When the unit 3 is moved from the water bath 11 to the cell 121 and also when the unit 3 is drawn up from the cells 121, 122, 123, 124, an air flow is applied to the unit 3 so as to reduce an amount of solution adhering to the unit 3. In this way, the solution adhering to the unit 3 can be removed. A deoiling agent is fed from the side of the cell 124 to the alkali bath 12 filled with an alkali washing solution. The washing solution that has overflowed the cell 124 flows into the adjacent cell 123. The washing solution that has overflowed the cell 123 flows into the adjacent cell 122. The washing solution containing oil is discharged from the cell 121 to the waste water treatment equipment 15. While the unit 3 is moved from the cell 121 to the cell 124, the adhering oil is gradually removed from the unit 3. After that, in the water bath 13 having cells 131, 132, 133 and into which washing water is fed from the cell 133, the washing solution adhered to the unit 3 in the alkali bath 12 is washed away. Finally, the unit 3 is heated and dried in the drying furnace 16. In this way, the deoiling process is completed. After the completion of the deoiling process, the unit 3 is assembled into a core 4 and brazed.
However, according to the water-soluble washing method described in method (1), a large amount of waste water is produced in the water bath 11, alkali bath 12 and water bath 13, which unpreferably causes various environmental problems. Further the water treatment equipment cost and the water treatment expense are relatively high.
According to the method described in method (2), since the high molecular component in the processing oil is difficult to evaporate, it becomes necessary to provide a heating apparatus in which heating is conducted in vacuum, or it is necessary to wash for replacing the processing oil with a light oil which can be easily evaporated, before conducting heating. As a result, the equipment cost and the material expenses are increased.
On the other hand, when a rate of processing is not so high, it is possible to use processing oil of low viscosity. In this case, the following methods (3) and (4) may be adopted.
It is possible to execute the above method (3) at atmospheric pressure when boiling points of the base oil and the additives contained in the processing oil are sufficiently low. The above method (4) is advantageous in that it is unnecessary to conduct heating. When the above methods (1) to (4) are compared with each other, the total cost including the equipment cost and energy cost can be reduced in the order of (1)&gt;(2)&gt;(3)&gt;(4).
However, the processing oil of low viscosity used in the above methods (3) and (4) is characterized in that the evaporating property is high at an ordinary temperature. Therefore, according to the conventional processing oil of low viscosity, when the apparatus stops for 2 to 3 days because of holidays, the processing oil evaporates, and lubricant starvation may be caused in the sliding sections of the die and others. Due to the foregoing, a friction coefficient between the die and the piece of work increases. Accordingly, there is a possibility that the sliding sections of the apparatus and the die are damaged when the die is repeatedly used. After the processing oil has evaporated, corrosion is caused in the die, and further oil necessary for the operation of the apparatus is removed. The above problems may be encountered according to the methods (3) and (4).
The present invention has been accomplished to solve the above problems. The first object of the present invention is to provide a heating deoiling apparatus in which adhering oil can be sufficiently removed from the work before the process of brazing by controlling the furnace temperature while ignition of adhering oil is prevented and a relative displacement of parts composing the work is suppressed.
The second object of the present invention is to accomplish the above first object while the fuel consumption is reduced and leakage of oil to the outside is prevented.
The third object of the present invention is to provide processing oil used for processing aluminum materials by which processing at a high rate can be conducted, and the processing oil can be removed by heating in the atmospheric pressure.
The fourth object of the present invention is to provide a processing oil for processing aluminum materials, the cost of which is low, and which can be removed by a deoiling method without affecting the natural environment.